Abstract

Leukoencephalopathy and autonomic dysfunction have been described in individuals with very low serum B12 levels (<200 pg/ml), in addition to psychiatric changes, neuropathy, dementia and subacute combined degeneration. Elevated
homocysteine and methylmalonic acid levels are considered more sensitive and specific for evaluating truly functional B12 deficiency. A previously healthy 62-year-old woman developed depression and cognitive deficits with autonomic dysfunction
that progressed over the course of 5 years. The patient had progressive, severe leukoencephalopathy on multiple MRI scans
over 5 years. Serum B12 levels ranged from 267 to 447 pg/ml. Homocysteine and methylmalonic acid levels were normal. Testing for antibody to intrinsic
factor was positive, consistent with pernicious anaemia. After treatment with intramuscular B12 injections (1000 μg daily for 1 week, weekly for 6 weeks, then monthly), she made a remarkable clinical recovery but remained
amnesic for major events of the last 5 years. Repeat MRI showed partial resolution of white matter changes. Serum B12, homocysteine and methylmalonic acid levels are unreliable predictors of B12-responsive neurologic disorders, and should be thoroughly investigated and presumptively treated in patients with unexplained
leukoencephalopathy because even long-standing deficits may be reversible.